Electric fuse and fuse receptacle



April 24, 1934. M B, WOOD 1,956,337

ELECTRIC FUSE AND FUSE RECEPTACLE Filed June l, 1933 Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE ELECTRIC FUSE AND FUSE RECEPTACLE Application June 1, 1933, Serial No. 673,851

7 Claims.

This invention relates to electric fuses, and especially to fuses of the screw plug type wherein the fusible element is contained within a screwthreaded plug or casing that is adapted to be screw-threaded into a socket or receptacle.

An electric fuse is intended primarily to protect the conductors of the circuit with which the fuse is in series against overheating due to the excessive loading thereof. With the increasing use of electrical appliances, circuits are frequently overloaded and blow fuses that are of a size or capacity adapted for the circuit conductors with the result that often it is replaced by a fuse of a larger capacity. This permits the excessive current to be carried but also permits the circuit conductors to be overloaded. Thus the practice of inserting a fuse of a larger capacity than is warranted by the current carrying capacity of the conductors is an unsafe practice.

Hence an object of the present invention is the provision of an improved form of screw plug fuse, intended to be used only for a certain range of capacities, that is not readily interchangeable with a fuse plug adapted for a different range of capacities.

Another object of the invention is the provision of a fuse so arranged that the terminals ofthe receptacle in which the fuse is adapted to be received can not be bridged readily by a coin, tinfoil or the like which is frequently employed by users of current to restore the continuity of their circuits when a fuse blows and no replacement fuse is available.

A further object is generally to improve the construction of electric fuses.

Fig. 1 is a sectional elevation of a fuse plug receptacle and a fuse plug therein embodying the present invention.

Fig. 2 is a plan view of the receptacle of Fig. l, with the fuse plug removed.

Fig. 3 is a side elevation of the fuse plug.

Fig. 4 is a view similar to Fig. 3 but illustrating a slightly modified form of plug.

Fig. 5 is a perspective view of the retaining shell.

Fig. 6 is a perspective View of the conical insulating member retained by the shell of Fig. 5.

Fig. 7 is a sectional detail similar to Fig. 1 but illustrating one of the positions that can be assumed by the loose insulating member.

Fig. 8 is a sectional detail illustrating the position of the fuse plug at the start of entering the insulating member.

Fig. 9 is a sectional detail of the fuse receptacle 55 illustrating the manner in which an ordinary fuse plug is prevented from being inserted in the receptacle.

Fig. 10 is a sectional detail through a locking tongue of the retaining shell of Fig. 5.

The fuse receptacle 10 is provided with an annular neck 12 in which is located an internallyscrew-threaded metal shell 14 that constitutes a terminal of the receptacle. The receptacle has a center contact 16 which is disposed within the shell at the bottom thereof. The fuse embodying the present invention includes a. metal retaining shell 18 having an inturned flange 20 at its upper end and wrench engaging recesses 22 or the equivalent in the flange in which the shell can be screw-threaded into the bottom part of the terminal shell 14. The shell is provided with outwardly projecting locking tongues; 24 which flex inwardly to permit the shell to be screwed within the terminal shell but rwhich dig into the terminal shell and prevent the rotation of the retaining shell 18 in an unscrewing direction. An insulating member 26 is located within said retaining shell and is held thereby against escape from the receptacle. Said insulating member is provided with a radially outstanding flange 28 which underlies the ilange 20 of the retaining shell and a conical body portion 30 that extends loosely through the opening surrounded by the flange 20 and projects above the shell a. substantial distance. Said insulating member is free for unrestricted lateral movement in any direction within the confines of the retaining shell and also for axial movement between the terminal contact 16 and the ilange 20 of the retaining shell and is capable of tilting in any direction in the manner illustrated in Fig. '1. Said insulating member is provided with a cylindrical passage 32 therein which extends from the top of the conical rmember through the base and opens above the center contact 16. The fuse also includes a fuse plug comprising a casing 34 having a bottom wall 36 that has a conical recess 38 therein that corresponds approximately with the shape of and is adapted to receive the conical portion 30 of the insulating member 26. The casing is also provided with a fuse compartment 40 and a. suitable cover 42 therefor. The casing 34 at the lower end thereof is also provided with an externally screwthreaded metal shell 44 that is adapted to engage the screw-threads of and enter the terminal shell 14 of the fuse receptacle. The casing 34 is provided with a center contact 46 in the form of a cylindrical rod which is provided with an enlarge contact head 48 at the lower end and an ing bridge between the terminals.

insulating tube above the head. Said tube bears upon the head at one end and against the bottom face of the conical recess 38 at the other end and is clamped therebetween by upsetting the upper end of the contact rod whereby to secure the contact rod rigidly in position in the bottom wall 36 in axial alignment with the screwthreaded shell 34 thereof. A fuse link 52 is connected to the upper end of the contact rod 46 and also to the shell 44 in more or less the usual manner. Said insulating tube 50 can be composed entirely7 of insulating material as fibre, as illustrated in Fig. l. Since for the present invention it is suflicient merely to have an insulating surface on the contact rod the tube 50 may be composed of a metal that has been treated to provide an insulating iilm 54 on its surface, as in Fig. 4. The tube, for instance, may be composed of metal that has been treated to provide an insulating film or aluminium oxide on its surface. An iron tube may be treated in an analogous manner to provide an insulating film. The film is integral with the metal composing the tube and has a sufficiently high dielectric strength to withstand the usual potentials to which the fuse is subjected. The center contact rod is adapted to be inserted in the passage 32 of the insulating member and to pass therealong into engagement with the center contact 16 of the fuse receptacle. The center contact of the fuse plug is adapted to project a substantial distance below the end of the fuse body 34 in such manner that when the end of the contact is just at the point of entering the passage 32 of the insulating member the screw-threaded shell 44 of the fuse plug is positively out of contact with the terminal shell 14 of the fuse receptacle so that it can not be screwed into the receptacle when any foreign material fills the passage 32. The center contact of the fuse plug is adapted to be a snug t in the passage 32 so that the contact and the insulating member 36 act as male and female dies to shear oi any conducting material, as tinfoil, that might be placed within the receptacle in an attempt to bridge the terminals. The contact head 48 of the center contact is of short axial length so that it can not be connected readily to the terminal shell by any bridging material that at the same time will permit the fuse plug to be screwed into the receptacle. The insulating member 26 is preferably loose or oating in its position above the center contact of the fuse receptacle so that it can align itself readily with the center contact of the fuse plug when the fuse plug is screwed home but will become tilted when a foreign material is crowded into the recess 32 of the insulating member or between the insulating member and the retaining shell and will thereby prevent the insertion of the plug in the receptacle to hold the material in terminal bridging position. The interiitting conical projection of the insulating member and the conical recess 38 of the plug render it difficult to retain and hold a conduct- The insulating member 36 also prevents a coin or other metallic disc from being positioned in terminal bridging position within the receptacle. The conical insulating member also projects upward toward the top of the receptacle a sufficient distance to prevent the ordinary fuse plug 56 from engaging the terminal shell 14 of the fuse receptacle, as is illustrated in Fig. 9. Thus the fuse receptacle is adapted to receive only the type of fuse plug herein described, which is intended for the lower capacities, and can not receive the ordinary type of fuse plug 56, which is intended for the higher capacities.

I claim:

1. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact, an insulating body overlying said center contact and having a conical portion which extends upwardly for a substantial distance and a passage which extends from the top of said conical portion through said body and is open above said center contact, and means retaining said insulating body in the aforesaid position within said terminal shell.

2. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact, an insulating body overlying said center contact and having a conical portion which extends upwardly for a substantial distance and a passage which extends from the top of said conical portion through said body and is open above said center contact, and means retaining said insulating body in the aforesaid position within said terminal shell, said means comprising a screw-threaded retaining shell which is screwthreaded into the bottom part of said terminal shell and has a retaining flange that overlies a part of said insulating body.

3. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact and a freely floating insulating body disposed within the bottom of said shell and over said center contact and having a conical part that extends upwardly for a substantial distance within said terminal shell and a tubular passage which extends downwardly from the top of said conical portion and is open above said center contact, and means which retains said insulating body in the aforesaid position and permits it to move laterally in any direction and also to tilt angularly in any direction.

4. The combination of a fuse receptacle having a screw-threaded terminal shell and a center contact, an insulating body located in the bottom of said terminal shell above said center contact having an outstanding flange and an upstanding conical portion and a tubular passage that extends from the top of said conical portion through said body and is open above said center contact, and a screw-threaded retaining shell for said insulating body that is screw-threaded into the bottom part of said terminal shell and has an inwardly directed flange that overlies and is spaced above the flange of said insulating body and is also spaced laterally of said conical part so that said insulating body is free for both lateral and angular movement in any direction.

5. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact and a floating insulating body located in the bottom of said shell above said center contact and having a passage therethrough which is open above said center contact, and a fuse plug having a body provided with a screw-threaded shell that is engaged with the screw-threads of said terminal shell and a center contact which extends beyond the end of said body and is extended through the passage in said iloating insulating body and is engaged with said center contact.

6. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact, an insulating body located within said shell and overlying said center contact and having an upwardly extended conical part and a cylindrical passage extending from top of said conical part through said body and open above said center contact, and a fuse plug comprising a body having a screw-threaded shell engaged with the screw threads of said terminal shell, a conical recess in its bottom wall, and a cylindrical center contact that projects from the middle of said conical recess beyond the end of said body and is snugly located within the passage of said insulating body in engagement with said center contact.

'7. The combination of a fuse receptacle having a screw-threaded terminal shell, a center contact, an insulating body located within said shell and overlying said center contact and having an upwardly extended conical part and a cylindrical passage extending from the top of said conical part through said body and open above said center contact, and a fuse plug comprising a body having a screw-threaded shell engaged with the screws-threads of said terminal shell, a conical recess in its bottom wall, and a cylindrical center contact that projects from the middle of said conical recess beyond the end of said body and is snugly located within the passage of said insulating body in engagement with said center contact, said insulating body being free for movement laterally within said receptacle and also being capable of tilting therein so that it can align itself with the center contact of said fuse body.

MORRIS B. WOOD. 

